The present invention relates to a head-up computer display and in particular to a head-up computer display having an increased contrast range and/or an increased range of colours that may be displayed.
So-called xe2x80x9chead-upxe2x80x9d displays are well known in many different areas of usage. An early usage of such head-up displays was for the presentation of flight, navigation and weapon information in an aircraft pilot""s line of sight. This allows the pilot to see such information whilst also looking in the direction of travel of the aircraft.
Wearable computing is an effort to make computers a totally integral part of our everyday lives by embedding computers into our clothing such as, for example, shoes, or by arranging computers that can be used like clothing, for example, sunglasses. This level of access to computation will revolutionise the applications for which computers are used. Typically, such computers are about the size of a palmtop computer with wires that attach to a display that sits in front of one or both eyes.
The display for a wearable computer is a head up type. The image is projected into the eye from a small display transducer such as a liquid crystal display (LCD) that is worn on the head. A deliberate design feature of this is that the user is able to see xe2x80x9cthroughxe2x80x9d the display to the environment behind, such as the office, home, outdoors and the like. The projected image from the wearable computer is added onto the user""s view of the environment and the projected image appears to xe2x80x9cfloatxe2x80x9d in space.
This works well for many projected images, but has the disadvantage that the maximum available contrast is determined by the ambient environment behind the projected image. For dark ambient environments the contrast range will be relatively high. However, in for example, brightly lit offices, the contrast range will be severely limited. Additionally, the display cannot show any black areas of the image as black. In order to display black, the liquid crystal display tries to entirely prevent the light from the backlight from being seen by the user, so no light image is projected at these points and thus the ambient light level predominates. Additionally, for a colour display, such an arrangement has the disadvantage that it cannot display low level primary (red, green or blue) or secondary (cyan, magenta, yellow) colours. Consequently, the visibility is determined by the ambient environment. For example, if such a display is used in a room with a predominantly red background, difficultly would be experienced in distinguishing low level red data generated by the display.
FIG. 1 shows a prior art display 100 for a wearable computer. The primary image source is a small LCD 102 with its own backlight. The image produced by the LCD 102 travels through a transparent block 104 (typically made of perspex or glass), through a beam splitter 106 and impinges on a mirror 108 at the end of the block. It is reflected from the mirror 108 and hits the beam splitter 106 again, where it is merged with the incoming light 110 from the environment and reaches the user""s eye 112.
This inability to display black or low intensity colours has far-reaching implications for the application of such displays to wearable computers. An extension to the display of FIG. 1 is to add a second display for the other eye. Since each eye may receive a different image, there is potential for stereoscopic or xe2x80x9c3Dxe2x80x9d images, that is, the images can have perceived depth. However, without some means of displaying dark colours, the contrast ratio is so reduced as to limit the usefulness and effectiveness of such a system in all but the darkest environments.
M G Tomilin, A P Onokhov, N T Firsov, xe2x80x9cNew eyeglass systems with local light protection from blinding objectsxe2x80x9d, J. Opt. Technol. (USA) Vol.64, No.5 May 1997 P489-92 discloses modifications of eyeglasses with local light protection of an observer""s eyes from blinding objects, based on the use of space time light modulators using liquid crystals operating in the transmission and reflection regimes. The purpose is to use a display device to replace conventional welding goggles. The object to be welded is viewed through an LCD and the visual field is light, enabling the welder easily to view the surroundings. When an arc is struck, its position in the visual field is identified by means of a photoconductor, using a beam-splitting device and the LCD is made opaque in that area, protecting the welder""s eyes.
So it would be desirable to provide an ability to display black or low intensity colours on the displays of wearable computers.
Accordingly, the present invention provides a display enabling a user to view a light emitting display and an ambient environment simultaneously, the display comprising: a light-transmissive block allowing the transmission of light from the ambient environment to the user""s eye through the block from a first surface to a second surface opposing said first surface; a light emitting display located on a third surface of the block, the third surface being substantially perpendicular to said first and second surfaces; a beam splitter having a plane surface arranged at substantially 45 degrees to said first and second surfaces, so as to reflect light from the light emitting display through the second surface; and a shutter, located on said first surface, adapted to block the transmission of light from the ambient environment to the user""s eye, for providing a dark background for the light emitting display.
This has the advantage that when a dark area is displayed on the light emitting display, the user sees a dark area instead of seeing the light from the ambient environment without a superimposed display.
Preferably, the display further comprises a mirror located on a fourth surface of the block, the fourth surface opposing said third surface.
In another embodiment, the shutter blocks the transmission of light from the ambient environment to the user""s eye when a dark background is selected for a window of a windowed operating system. Typically, the backgrounds of text applications and of computer games may be dark and so the present invention provides the advantage that these backgrounds are correctly displayed.
Another embodiment has the shutter adapted to block the transmission of light from the ambient environment to the user""s eye over the entire area of the shutter, thereby simulating a conventional desktop display.
Another embodiment has the shutter adapted to allow the transmission of light from the ambient environment to the user""s eye over the entire area of the shutter, thereby simulating a conventional head up display.
In an alternative embodiment, for each portion of the screen, the transmission of the shutter is directly dependent on the intensity of the light emitting display for that portion of the screen. This has the advantage of providing an enhanced contrast ratio for intermediate intensity levels.
Preferably, the shutter is arranged so as to be coincident with the image from the light emitting display.
Further preferably, the shutter has a number of pixels equal to that of the light emitting display, the pixels having the same apparent size as those of the light emitting display.
In an embodiment, the light transmission of the light-transmissive block outside the pre-defined area of the shutter is substantially greater than the light transmission of the shutter in its open state. This has the advantage that the user is aware of where the background of the projected image is, regardless of the background intensity of that projected image.
The invention also provides a display system comprising a display as described above for each of the eyes of a user.